INHIBITION OF GLYCOGENIN-CATALYZED GLUCOSYL AND XYLOSYL TRANSFER BY CYTIDINE 5'-DIPHOSPHATE AND RELATED-COMPOUNDS

The self-glucosylation of beef kidney glycogenin was inhibited by the following pyrimidine nucleotides and nucleotide sugars, listed in orde r of decreasing effectiveness: CDP-glucose, CDP, UDP-xylose, UDP-N-ace tylglucosamine, UDP-galactose, UDP, CTP, CDP-choline, UDP-glucuronic a cid, beta-S-UDP-glucose, and CMP. In contrast, the purine nucleotide s ugars, ADP-glucose and GDP-glucose, were essentially ineffective, as w as the pyrimidine nucleoside, cytidine. UDP-Xylose may be utilized by glycogenin as an alternative sugar donor instead of UDP-glucose (Roden , L., Ananth, S., Campbell, P., Manzella, S., and Meezan, E. (1994) J. Biol. Chem. 269, 11509-11513) and therefore presumably inhibited the glucosyl transfer reaction by being a competitive substrate. Like gluc osyl transfer, xylosyl incorporation into glycogenin was also inhibite d effectively by CDP. On the other hand, UDP-xylose:proteoglycan core protein xylosyltransferase (EC 2.4.2.26) was not affected by CDP, nor was it inhibited by UDP-glucose. Addition of CDP or UDP-glucose to rea ction mixtures containing both enzymes therefore made it possible to a ssay xylosyltransferase EC 2.4.2.28 reliably without the extensive pro duct characterization that is otherwise necessary. The CDP effect on g lycogenin further allowed the development of an improved procedure for the purification of this enzyme, in which specific elution of an affi nity matrix (UDP-glucuronic acid-agarose) was carried out with CDP as the eluant. (C) 1995 Academic Press, Inc.